def find_diff(s1, s2):
    s1_list = list(s1)
    s2_list = list(s2)
    for s in s1_list:
        if s in s2_list:
            s2_list.remove(s)
    print(f'"{s2_list[0]}"是那个被添加的字母')


def find_diff2(s1, s2):
    for s in s2:
        if s not in s1:
            print(f'"{s}"是那个被添加的字母')
            break


if __name__ == '__main__':
    s1 = 'abcd'
    s2 = 'abcde'
    find_diff(s1, s2)
    find_diff2(s1, s2)
